Spark plasma sintering of W-10Ti high-purity sputtering target: Densification mechanism and microstructure evolution

The densification mechanism and microstructure evolution of W-10Ti sputtering target prepared by spark plasma sintering (SPS) method at a temperature ranges from 900 to 1600 degrees C, with dwelling time of 6 min and fixed pressure of 30 MPa were investigated. Densification occurs mainly at low temperatures (900 to 1300 degrees C), while grain growth occurs at high temperatures (1400 to 1600 degrees C). The creep model has been used to reveal the densification process. The effective stress exponent n is calculated systematically, which indicates that the densification process is mainly due to the particle rearrangement (n < 1), grain boundary diffusion (n = 1-2), and dislocation climbing (n = 3.77 or 4.14). In addition, the apparent activation energy Q(d) is calculated to be 119.30 and 271.79 kJ/mol when the effective stress exponent n is equal to 1 and 2, respectively. It is also found that the microstructure of W-10Ti alloys is greatly affected by the sintering temperatures. The solution between W and Ti significantly improves with the increase of the sintering temperature. The solubility of W in beta Ti(W) exceeded the eutectoid point (28.97 wt% W) and the eutectoid structure (beta W(Ti) + alpha Ti) forms in cooling process when the temperature is up to 1300 degrees C. With the temperature increasing to 1500 degrees C, the composition of the beta Ti(W) phase is located in the miscibility gap of the (beta Ti(W), beta W(Ti)) system, which tends to decompose in to beta Ti(W) and beta W(Ti) phases.